with this sort of setup, i'd stick to track use. not just "mainly," but exclusively. don't resist, you might spin the cog off. jb weld or red loctite might hold up against resisting, but you never know...
anyway, if it's for track use, there's also the rotafixa method of securing a track cog w/o a lockring. seems to me in one fell swoop you can secure the track cog onto the threaded adaptor, and the adaptor to the hub, all in one fell swoop:
http://204.73.203.34/fisso/eng/schpignone.htm
however, you might be able to pull the cog off the adaptor... or the adaptor off of the hub... but i'm not sure if you could do both easily. and if the cog comes off the adaptor, you might have an awful tough time getting the adaptor off the hub...